LED and OLED lighting panels offer many advantages for general lighting purposes. They are efficient in terms of light output for power consumed. They are low voltage which helps avoid potential electrical shocks, less prone to sparking in potentially explosive environments and reduce loads in the supporting electrical system. The spectrum of emitted light can be varied using appropriate internal designs. They produce little or no UV or IR light. They are instant on; that is, they emit light immediately whenever electrical power is supplied. LED light sources are inherently small point sources and in order to serve as a flat general lighting source, many separate LED devices must be ganged together. This raises manufacturing costs and complexity. Uniformity of the light surface must be controlled by appropriate design. LEDs produce some heat and so, heat sinks or other thermal control measures are often employed. Practical LED lighting panels can be made very thin, for example as thin as 3-16 mm, with appropriate system design. OLED light sources are inherently flat area light sources. They offer several advantages over LED lighting panels. They can be made even thinner (for example, less than 1 mm thick) and they produce very little heat under normal operating conditions. However, OLED lifetimes can be an issue. Both LED and OLED lighting panels can be made on flexible or curved substrates even though OLED is preferred for these types of applications. In summary, both LED and OLED lighting panels can be useful as lighting panels. They are both efficient, low voltage, cool to the touch, and are thin. Luminaires (a complete unit with a light source (i.e. a lamp) and a support unit (i.e. a lamp holder) that provides light and illumination) can be designed to utilize flat LED or OLED lighting panels.
Although OLED lighting panels have many desirable properties over LED panels, they currently have significantly higher manufacturing costs. In order to increase the penetration of lighting markets and make OLED lighting more cost-competitive to LED lighting, there is a great need for improved manufacturing processes that will lower overall OLED manufacturing costs.
In general, white light emitting OLED panels have multiple organic layers which are responsible for light emission between two electrodes of opposite charge; all located on a substrate. One of the electrodes must be at least semi-transparent. When power is supplied to the electrodes, light is emitted. Because the organic layers are sensitive to air and water, the OLED must be encapsulated; however, electrical connections to the electrodes must still penetrate through the encapsulation. Even in the simplest OLED structures, at least some layers must be patterned; for example, the two electrodes must never come in contact with each other and so, they must be patterned during manufacture so there is no direct contact. In most cases, organic layers cannot be deposited in or over the sealing region of the encapsulation since organic layers are not sufficiently air and water impermeable. Thus, these layers must be patterned to some degree as well.
Because OLEDs are composed of multiple overlapping layers of different materials on a substrate, each layer must be deposited separately and so, the manufacture of the entire OLED requires a large number of steps to complete the device. The electrode layers, which are typically inorganic (i.e. metals or metal oxides), are typically deposited by sputtering techniques. There are two general methods for depositing the organic OLED layers; vapor deposition vacuum or coating from solution. Each of these methods have advantages and disadvantages. Vapor deposition is based on heating the material(s) to be deposited under high vacuum and directing the resulting vaporized material onto the deposition surface. This creates layers of the materials(s) that are generally free from contamination. The organic materials must be thermally stable at their vaporization temperature. However, this method is wasteful in terms of the amount of material actually deposited which leads to higher costs since the OLED materials can be very expensive. Moreover, the rate of material deposition can be relatively slow, leading to long manufacturing times. Finally, the high vacuum equipment required for this method is complex, difficult to maintain and expensive.
For sputtering or vacuum deposition, shadow masks can be used if patterning is necessary. However, the use of shadow masking can be problematic. The masks are thin with fine features and so are expensive to prepare. Moreover, build-up of vaporized material on the masks can be problematic and cleaning them is difficult and time consuming. The useful lifetime of the masks is also limited. Moreover, changing of shadow masks from one step to another can create extraneous particles which can lead to contamination and problems with layer uniformity and shorting during later steps.
Solution coating is based on using OLED materials either in liquid form (i.e. polymers) or soluble in a solvent. The liquid is coated uniformly over the surface and then solidified by solvent removal or other processes. This method has low material waste, the layer can be deposited relatively quickly and the equipment required is relatively simple, but it is very prone to contamination. This leads to variability in terms of efficiency, uniformity and lifetime. Patterning can be accomplished via methods such as ink-jet or screen printing if necessary.
No matter what kind of deposition method is used, it is very desirable to have an in-line production machine where a raw substrate is completely converted to a finished OLED in order to minimize costs. However, because it is necessary to deposit multiple layers, some of which may be patterned, there will generally be many stations along the manufacturing line, each dedicated to a specific step or group of steps. This leads to a complicated equipment line and high capital costs.
One way to minimize costs and decrease complexity of the equipment is to use a “roll-to-roll” system. In a “roll-to-roll” system, a flexible substrate is mounted on a roll on one end of the equipment, then is unrolled and passed through, as a continuous web, the various processing stations to add the OLED layers, and the finished OLED is then rolled up on the end of the equipment. This would require the use of a flexible substrate that would be stable to the various processing steps and be air and water impermeable (since it would be part of the final encapsulation). However, it avoids the complexity of trying to transport a rigid substrate (which necessarily would be in separate, non-continuous sections) throughout many stations. Hybrid systems using individual rigid substrates temporarily mounted on a flexible moving web are known.
For at least these reasons, it would be desirable to develop an in-line OLED manufacturing process which avoids or minimizes the number of masking steps when using vapor deposition or sputtering methods to form the layers, preferably in a roll-to-roll process. Not only would the production equipment be less complex, easier to maintain and have lower capital costs, elimination of shadow masks would lead to still lower costs as well as avoiding mask cleaning. However, even partial elimination of the number of steps requiring shadow masking would still be very advantageous for manufacturing OLEDs. This would apply to both “roll-to-roll” processes as well as non-continuous processes using rigid substrates.
As mentioned previously, the OLED needs to be encapsulated by air- and moisture-proof materials. This can be problematic in a “roll-to-roll” process where a completely finished and fully encapsulated OLED panel is the end product of the production line. This is because while the raw substrate is a continuous roll, the OLED panel is not and will have a finite length. This means that at some point in the overall process, it will be necessary to cut the substrate and its overlying layers perpendicular to the length of the continuous web. This will create side edges of the layers which must be encapsulated. Thus, in such processes, the unfinished OLED web is cut before encapsulation and then encapsulated in a later process. This adds complexity and cost back into the manufacturing process. For this reason, it would desirable to allow for an encapsulation process directly on the continuous OLED web where when the OLEDs are cut into individual sections, the side edges of the various layers are not revealed and remain encapsulated.
It is well known to use solder as a hermetic solder seal for electronic packages in order to protect them from air and water infiltration. A hermetic seal or closure is complete, waterproof and airtight. Generally speaking, a solder seal should be substantially inorganic and not contain significant amounts of organic materials. It should be thermally mobile and is not cured by radiation or curing agents.
There are generally two types of solder used for hermetic sealing. The first type of solder is a low melting alloy of metals, which when melted, can flow between different components and fill up the space between them, thus forming a seal. Often, the exact composition of the solder can be manipulated to improve its properties for the application. The second type is glass frit bonding where glass solders are used to join glasses to other glasses, ceramics, metals, semiconductors, mica, and other materials. Two types of glass solders are used: vitreous, and devitrifying. Vitreous solders retain their amorphous structure during solidifying whereas devitrifying solders undergo partial crystallization during solidifying. Low temperature glass solders are known.
For example, U.S. Pat. No. 3,472,640 describes locally heating a long strip of glass frit solder to make a seal between two glass plates. U.S. Pat. Nos. 3,508,209, 3,429,040, 3,495,133 and 4,081,901 all describe the use of a glass barrier layer to control the spreading/wetting of solder along a conductive electrode. U.S. Pat. No. 5,385,499 describes encapsulation using a pattern of glass frit in a photoresin, followed by heating to remove organics. U.S. Pat. No. 5,825,086 describes putting a metal layer on a top ceramic sealing plate in order to improve solder wetting between a bottom glass plate and the top ceramic plate. U.S. Pat. No. 6,531,663 describes the use of a solder stop (inorganic particles in a weak glass matrix) over a conductive layer to control solder wetting. U.S. Pat. No. 6,614,057 describes side encapsulation using two barrier layers; the outer can be solder, the inner epoxy resin. U.S. Pat. No. 8,518,727 describes side encapsulation with two barrier layers, the outer can be glass frit, the inner UV curable resin. U.S. Pat. No. 9,545,682 describes side encapsulation between glass plates using glass frit solder. There may be an outer dam of glass. US20170055348 describes the use of a wick stop to control solder wetting on a conductive layer. The wick stop is non-wetting and can be an insulating material such as glass. JP2000-223263 describes the use of ultrasonic welding for hermetic sealing of OLEDs. F. M. Hosking et al, “Soldering of Thin Film-metallizing Soda-Lime Glass Substrates’, 1999 discusses methods for sealing glass plates with solder in solar cells.